RAS TANURA, SAUDI ARABIA, SEPT. 3 -- Security has been tightened around the Middle East's largest oil exporting terminal here, and the order has gone out to the giant refinery to step up production, particularly of such strategic products as jet fuel.

Otherwise, a visitor to what may be the most critical facility anywhere in the world now to the West's economic well-being would scarcely sense that Ras Tanura is a focus of intense Saudi and American defense preparations, with more than 50,000 U.S. troops taking up positions near here to protect it and other Saudi oil installations from possible Iraqi attack.

Saudi Arabia has boosted its crude oil production by 2 million barrels a day to help make up for the loss of the 4 million barrels that Iraq and Kuwait, now occupied by Iraq, once exported. But the number of oil tankers calling here has not increased.

Today, just four ships, including the Johar out of Karachi, Pakistan, and the Panamanian World Sky, were in port taking on crude oil, liquid natural gas and other products.

"It will probably take two to three weeks to see the difference," said Mohammed Yonas, the chief harbor pilot, who hastily returned from vacation in Switzerland when Iraq invaded Kuwait last month.

The biggest immediate change has been in the Ras Tanura refinery's production, from 310,000 barrels a day in July to 460,000 barrels now -- still short of the 530,000 capacity that makes it the biggest plant in the Persian Gulf.

Perhaps the most telltale sign of the times, however, is the big increase in production of JP-4 jet fuel that Saudi and U.S. warplanes need to provide round-the-clock surveillance of Iraqi air and land movements. The refinery has boosted its output of this crucial product from 2,000 barrels a day to 5,000.

Kuwaiti refineries used to provide the bulk of the Arab gulf states' need for JP-4. Iraq's capture of Kuwait has meant, among other things, the loss of the main source of jet fuel for the region.

The Saudi government brought about 60 television, radio and newspaper reporters to what are probably the kingdom's most sensitive oil facilities as part of its new policy of openness toward the Western press and apparently, too, to illustrate that normalcy prevails despite the war jitters.

Television cameramen and photographers were allowed to take as many pictures of the facilities as they wanted, although a bevy of security personnel kept a close eye on their activities.

The port and refinery have been under heavy guard and defense, including an antiaircraft missile site, ever since the Iran-Iraq war, when Iranian propaganda threatened the kingdom's oil facilities with terrorist and other retaliation for its support of Iraq.

Frontier Forces security men searched reporters' bags and checked for hidden bombs underneath the two buses that brought them. But employees said that closer checks at the entrance gate and more armed patrols were the main noticeable change in what was already a very high security area.

Ras Tanura was once a far busier oil export terminal. Yonas said he still remembers the early 1980s when at least 10 million barrels a day were being pumped out to the 25 onshore and offshore loading platforms here and nearby. In those days, 350 tankers a month called here, compared to an average 170 this year, picking up only 3.7 million barrels daily in July.

The terminal probably will never see such business again. The Saudi government has since built two 745-mile pipelines across the desert kingdom to Yanbu, on the Red Sea, allowing it to export up to 3.2 million barrels a day from there.